The present invention relates generally to a control system for a fuel burner and more particularly to a low voltage control system of the direct ignition type.
In the past, control systems for fuel burners, such as gas furnaces or the like, typically provided a thermostat to open a fuel valve when the thermostat indicated a demand for heat and also typically provided means for automatically igniting fuel emitted from the burner. Ignition may have been achieved by a small pilot flame which burned continuously or may have achieved by using a spark or arc ignitor which provided a spark in the vicinity of the burner at about the same time or soon after the fuel valve was opened.
Recent improvements in burner control units of the abovementioned type are well illustrated by U.S. Pat. No. 3,734,676 which discloses a control system for a fuel burner. In this patented control system, an ignitor and a controlled switching device are effective when gated to connect the ignitor to a source of electrical energy for providing pulses of electrical energy to the ignitor. This patented control system has a gate circuit including a capacitance for providing gate signals to the controlled switching device. These gate signals are provided so long as the capacitance has a charge below a specified level and the capacitance is initially provided with a charge above that specified level. The capacitance charge is reduced with time so as to gate the controlled switching device to operatively connect the ignitor to a source of electrical energy only after a predetermined period of energization of the control system thereby to effect pre-ignition purging of the burner area to insure there is not an over abundance of fuel when ignition occurs.
Control systems of the type illustrated in the aforementioned U.S. patent function quite well but may be thought of as typically operating on a 120 volt alternating current supply or employing a step-up transformer from the commonly encountered low voltage thermostat systems which typically operate around 24 volts A.C. Control system according to the aforementioned patent and the aforementioned copending application function well but may not lend themselves to some particular applications, such as mobile heating environments or the like where direct current or optional alternating current-direct current operation is desirable.